While detecting fingerprints, a fingerprint sensor may generate inaccurate sensing results due to noise in the power source or in the environment. To reduce such noise interference, many methods can be used nowadays. For example, the circuits in a fingerprint sensor and the finger whose fingerprint is to be sensed can be provided with the same ground potential by a common ground plate in order to eliminate some of the noise. However, the use of a common ground plate requires additional steps in the sensor manufacturing process, incurs extra cost, and takes up certain space. This is why common ground plates are no longer suitable for use when the volume of circuits is gradually reduced.
U.S. Pat. No. 7,460,697 reduces noise interference by adding more sensing plates, but this approach is costly and complicates the sensor manufacturing process even more. U.S. Pat. No. 8,787,632 reduces noise interference by sensing fingerprints while noise is relatively low, but the avoidance of noise prolongs the sensing time. U.S. Pat. No. 4,811,414 uses an averaging method to reduce noise interference, and yet the fluctuation of noise over time makes it impossible to reduce noise interference effectively. It has also been proposed to eliminate the noise in the sensing data of each sensing plate by an oversampling or averaging method, but the sensing time required to obtain fingerprint data from all the sensing plates will be exceedingly long.
Therefore, it is desired a more effective and simpler method for reduction of noise interference for fingerprint sensing.